CN111745324A

CN111745324A - Solder paste and mounting structure

Info

Publication number: CN111745324A
Application number: CN202010193677.7A
Authority: CN
Inventors: 铃木康宽; 日野裕久; 山津繁
Original assignee: Panasonic Intellectual Property Management Co Ltd
Current assignee: Panasonic Intellectual Property Management Co Ltd
Priority date: 2019-03-28
Filing date: 2020-03-18
Publication date: 2020-10-09
Also published as: US20200306893A1; JP2020163404A; JP7126167B2

Abstract

The purpose of the present invention is to provide a solder paste that can be applied to solder joints that require a high melting point and that has excellent coating workability, high adhesion, and excellent solder joint reliability, and a mounting structure that uses the solder paste and that mounts electronic components. The solder paste is a solder paste containing solder powder and a flux, the flux containing an epoxy resin, a phenolic resin, a benzoxazine compound and an active agent, and the phenolic resin containing 1 or more phenolic resins having a phenolic hydroxyl group and an allyl group in a molecule.

Description

Solder paste and mounting structure

Technical Field

The present invention relates generally to a solder paste and a mounting structure in which epoxy resin is contained in a flux component in a solder paste used when a semiconductor component, an electronic component, or the like is soldered to a circuit board.

Background

In recent years, mobile devices such as mobile phones and pdas (personal Digital assistants) have been reduced in size and improved in functionality. As a mounting technique that can cope with this, a mounting structure such as bga (ball Grid array) or csp (chip Scale package) is often used. Mobile devices are easily exposed to mechanical loads such as drop shock. In the case of qfp (quad Flat package), the lead portion absorbs the impact. However, it is important to ensure impact-resistant reliability for BGA, CSP, and the like that do not have a lead for shock absorption. In particular, with recent high functionality and high power of conductor devices, heat cycle resistance and heat resistance have become important. In vehicle-mounted applications, strict vibration resistance and heat resistance are required for mounting semiconductor devices in an engine room. Therefore, high solder connection reliability in device mounting is becoming essential, and a structural method and a solder material capable of achieving the object are desired.

As a structural method for improving the connection reliability of solder, an underfill material is used for mounting BGA and CSP. The mounting structure using the underfill material means: a method of connecting an electronic component and a circuit board by melting a solder ball (for example, Sn — Ag — Cu solder ball), and filling the periphery of the solder with an epoxy resin or the like. The electronic component subjected to underfill can disperse external forces such as thermal expansion and contraction, vibration, and dropping stress to the surrounding resin without concentrating on the solder by covering the periphery of the solder with the resin. Therefore, high connection reliability can be exhibited. However, this mounting method requires that the underfill material be filled into a gap between the electronic component and the circuit board of about several tens of micrometers by capillary force. For this reason, the installation time per equipment becomes long. Further, since the underfill material is thermally cured after filling, the process becomes longer, and the cost becomes higher.

As a further measure, a semiconductor mounted structure using a solder paste containing a thermosetting resin in a flux and a method for manufacturing the same have been proposed (see, for example, patent document 1).

In a step of heating and melting solder to connect solder, a reinforcing structure in which the resin covers the periphery of the solder can be formed by separating the resin contained in the flux from the solder. As a result of this reinforcement, the strength of the connection portion of the solder can be improved.

In the mounting process using the solder paste, the wiring electrodes of the circuit board and the like are printed at predetermined positions using a metal mask, and then heated in a reflow furnace. In this case, the flux exhibits an effect of chemically removing the oxide film on the surface of the metal to be soldered and the oxide film on the surface of the solder powder by a reduction reaction, that is, a flux effect, and the solder can be fused and connected. Thereafter, a thermosetting resin such as an epoxy resin was cured, and the wiring electrodes of the circuit board and the electronic components were bonded and reinforced with the resin by 1 heat reflow step.

On the other hand, as a solder material, Pb eutectic solder has been typically used in the past, but recently, lead-free solder has been used from the viewpoint of environmental protection. For example, the lead-free solder includes Sn-Bi solder, Sn-Ag-Cu solder (hereinafter also referred to as SAC solder), Sn-Cu solder, and the like. In mounting using SAC solder or the like, In-containing solders or the like having different metal compositions have also been put into practical use as a measure for achieving high connection reliability. As a representative example of SAC solders, SAC305(Sn-3.0Ag-0.5Cu) solder (hereinafter also referred to simply as SAC305 solder) and SAC105(Sn-1.0Ag-0.5Cu) solder (silver ratio is 1%) having a lower silver ratio (hereinafter also referred to simply as SAC105 solder) have been studied and put into practical use.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 5204241

Disclosure of Invention

Problems to be solved by the invention

As described above, according to the solder paste including the thermosetting resin in the flux, the connection reliability can be improved by the reinforcing structure formed of the resin without causing a process delay and a cost problem. However, a product put into practical use by such a solder paste uses a low melting point solder such as Sn — Bi solder as shown in patent document 1. For example, a solder paste containing a thermosetting resin and using a high melting point solder such as SAC solder has not been practically used.

Specifically, in the case of the low melting point Sn — Bi solder shown in patent document 1, the melting point is about 139 ℃, and thus, after the solder is melted, the epoxy resin, which is a thermosetting resin, is cured. Therefore, the solder joint portion (conductive portion) and the resin reinforcing portion can be formed appropriately. On the other hand, in order to sufficiently melt SAC305 solder having a melting point of about 219 ℃ in a reflow process, it is necessary to increase the peak temperature of a reflow furnace to 240 to 260 ℃. In general, an epoxy resin as a thermosetting resin in a flux of a solder paste starts a curing reaction at 100 to 150 ℃. Therefore, in the reflow process, before the solder particles dispersed in the solder paste melt and aggregate, the epoxy resin starts to solidify and thicken, and it is difficult to appropriately form solder joints and the like. Further, the epoxy resin has a very high curing rate at a high temperature of about 200 ℃ compared with a temperature of about 150 ℃, and is cured in a short time. Therefore, particularly in the case of a high melting point solder, it is very difficult to form the solder bonding portion and the resin reinforcing portion with a solder paste containing a thermosetting resin.

As described above, a solder paste capable of appropriately forming a solder joint portion and a resin reinforcing portion even when a reflow process by a high melting point is performed is desired.

Accordingly, an object of the present invention is to provide a solder paste which is applicable to solder connection requiring a high melting point and has excellent coating workability, high adhesion, and excellent solder connection reliability, and a mounting structure on which electronic components are mounted using the same.

Means for solving the problems

In general, even when a mixture containing only an epoxy resin and a phenol resin is heated at a high temperature of, for example, about 240 ℃ for 1 hour without containing a curing accelerator used for curing the epoxy resin in a low temperature region around 150 ℃, the resin is hardly cured. However, it can be seen that: by adding an appropriate amount of benzoxazine compound to this mixture, resin curing occurs at a high temperature of about 240 ℃ in a short time of about several minutes. Furthermore, it can be seen that: in order to exert the flux action, a suitable solder paste can be obtained by further adding an appropriate amount of an activator to the mixture to which the benzoxazine compound is added. And it can be known that: the inclusion of the phenol resin having an allyl group significantly improves the adhesion of the cured product.

According to a first aspect of the present invention, there is provided a solder paste comprising solder powder and flux,

the soldering flux comprises epoxy resin, phenolic resin, benzoxazine compound and an active agent,

the phenol resin contains 1 or more kinds of phenol resins having a phenolic hydroxyl group and an allyl group in the molecule.

In one aspect of the first aspect of the present invention, the ratio of the number of moles of epoxy groups contained in the epoxy resin to the number of moles of the phenolic hydroxyl groups to the number of moles of the dihydrobenzoxazine rings contained in the benzoxazine compound may be:

(the molar ratio of epoxy groups to (the molar ratio of phenolic hydroxyl groups) to (the molar ratio of dihydrobenzoxazine rings) is 100: 50 to 124: 6 to 50.

In the above aspect of the first aspect of the present invention, the sum of the number of moles of the epoxy group, the number of moles of the phenolic hydroxyl group, and the number of moles of the dihydrobenzoxazine ring may satisfy the following formula:

{ (the number of moles of phenolic hydroxyl groups) + (the number of moles of dihydrobenzoxazine rings) }/(the number of moles of epoxy groups) } is 0.5 or more and 1.3 or less.

In one aspect of the first aspect of the present invention, the phenol resin may include a phenol resin having no allyl group in an amount of 40 mass% or less with respect to the entire amount of the phenol resin.

In the first aspect of the present invention, the benzoxazine compound may be a poly-oxazine having a plurality of dihydrobenzoxazine rings in the molecule.

In one embodiment of the first aspect of the present invention, the solder powder may be Sn — Ag — Cu based solder or Sn — Cu based solder having a melting point of 200 ℃.

In one aspect of the first aspect of the present invention, the solder powder may be contained in a proportion of 5 mass% or more and 95 mass% or less with respect to the total mass of the solder paste.

In one embodiment of the first aspect of the present invention, the reaction mixture may further contain a reactive diluent,

the reactive diluent may be 1, 3-bis [ (2, 3-epoxypropyl) oxy ] benzene.

In one embodiment of the first aspect of the present invention, the active agent may be an organic acid,

the melting point of the organic acid may be 130 ℃ or higher and 220 ℃ or lower.

According to a second aspect of the present invention, there is provided a mounting structure for mounting an electronic component on a circuit board using the solder paste according to the first aspect, the mounting structure including:

a conductive portion formed by metal bonding the electronic component and the circuit board; and

and a reinforcing portion formed by covering the periphery of the conductive portion with a cured product of the flux.

Effects of the invention

The solder paste according to the present invention is also applicable to solder connection requiring a high melting point, and has excellent coating workability, high adhesion, and excellent solder connection reliability.

Drawings

Fig. 1 is a sectional view of a solder bonding portion of a CSP bonded with a solder paste in an embodiment of the present invention.

Fig. 2A is a cross-sectional explanatory view schematically showing a bonding process of the ball portion of the CSP using the solder paste in the embodiment of the present invention.

Fig. 2B is a cross-sectional explanatory view schematically showing a bonding process of the ball portion of the CSP using the solder paste in the embodiment of the present invention.

Fig. 2C is a cross-sectional explanatory view schematically showing a bonding process of the ball portion of the CSP using the solder paste in the embodiment of the present invention.

Fig. 2D is an image of a cross section of a solder bonding portion of the CSP bonded with the solder paste in the embodiment of the present invention.

Fig. 3A is a cross-sectional explanatory view schematically showing a chip component bonding process using the solder paste in the embodiment of the present invention.

Fig. 3B is a sectional explanatory view schematically showing a chip component bonding process using the solder paste in the embodiment of the present invention.

Fig. 3C is a sectional explanatory view schematically showing a chip component bonding process using the solder paste in the embodiment of the present invention.

Fig. 4 is a table showing the formulation, characteristics and comprehensive judgment of the solder pastes of example 1 to example 10 in the embodiment of the present invention.

Fig. 5 is a table showing the formulation, characteristics and comprehensive judgment of solder pastes of comparative examples 1 to 3 in the embodiment of the present invention.

Fig. 6 is a schematic cross-sectional view illustrating a method of measuring shear adhesion force of a chip component.

Fig. 7 is a graph showing the measurement results of the shear adhesion force of the chip component in the example of the present invention.

Description of the reference numerals

1 CSP substrate

2 electrode

3 Circuit board

4 electrodes

5 conductive part

6a epoxy resin (uncured liquid)

6b reinforcing part

7 solder paste

8 solder ball

9 drier

10 chip component

11 conductive part

12 shear clamp

13 platform

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

The solder paste in the embodiment of the present invention contains solder powder and flux. Fig. 1 is a sectional view of a solder bonding portion of a CSP bonded with a solder paste in an embodiment of the present invention. As shown in fig. 1, the following structure is presented: electrodes 2 provided on the CSP substrate 1 and electrodes 4 provided on the circuit substrate 3 are bonded to each other by a conductive portion 5 including a melted portion of a solder ball and a portion derived from solder powder, and the periphery thereof is reinforced by a reinforcing portion 6b which is a solid epoxy resin obtained by curing a flux.

The composition of the solder paste according to the embodiment of the present invention will be described in detail below.

The solder paste in the embodiment of the present invention contains solder powder and flux, and may contain other components as necessary. The flux comprises an epoxy resin, a phenolic resin, a benzoxazine compound and an active agent.

< flux >

The flux in the solder paste in the embodiment of the present invention includes an epoxy resin, a phenol resin, a benzoxazine compound, and an activator, and the phenol resin includes 1 or more kinds of phenol resins having a phenolic hydroxyl group and an allyl group in a molecule. By including the flux in the solder paste of the present invention with such a composition, excellent coating workability, high adhesion of the solder paste, and excellent solder connection reliability and stable conductivity of the joint portion can be effectively achieved.

The amount of the flux is preferably 5 mass% or more and 95 mass% or less with respect to the total mass of the solder paste. When the content of the flux is 5% by mass or more, the flux action can be appropriately generated at the time of solder bonding. When the content of the flux is 95 mass% or less, the printability is appropriate, and the bonded portion based on the remaining solder powder can have stable conductivity.

Hereinafter, each essential component included in the flux is described in more detail.

(epoxy resin)

The epoxy resin is generally a thermosetting resin that has an epoxy group in its structure and can be cured by heating. In the embodiment of the present invention, the epoxy resin (base epoxy resin) included in the flux is liquid at normal temperature. By blending such an epoxy resin, other components such as solder particles can be easily dispersed. In the present specification, "liquid at ordinary temperature" means: has fluidity in a temperature range of 5 ℃ to 28 ℃ under atmospheric pressure, particularly at room temperature of about 20 ℃. Alternatively, the epoxy resin may be liquefied by mixing a solid epoxy resin with a liquid epoxy resin at normal temperature.

As the epoxy resin which is liquid at ordinary temperature, as long as it has 2 or more epoxy groups in 1 molecule, the molecular weight and molecular structure thereof are not particularly limited, and various resins can be used. Specifically, various liquid epoxy resins such as a glycidyl ether type, a glycidyl amine type, a glycidyl ester type, and an olefin oxide type (alicyclic type) can be used. More specifically, bisphenol type epoxy resins such as bisphenol a type epoxy resin and bisphenol F type epoxy resin; hydrogenated bisphenol epoxy resins such as hydrogenated bisphenol a epoxy resin and hydrogenated bisphenol F epoxy resin; biphenyl type epoxy resin, naphthalene ring-containing epoxy resin, alicyclic epoxy resin, dicyclopentadiene type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, triphenylmethane type epoxy resin, aliphatic epoxy resin, triglycidyl isocyanurate, and the like. These may be used alone in 1 kind, or in combination of 2 or more kinds. Among these, bisphenol epoxy resins and hydrogenated bisphenol epoxy resins are preferable as epoxy resins that are liquid at room temperature, in view of the reduction in viscosity of the liquid epoxy resin composition for encapsulating semiconductors and the improvement in physical properties of the cured product. Specifically, commercially available products include bisphenol A epoxy resin (model jER828 manufactured by Mitsubishi chemical corporation) and bisphenol F epoxy resin (model jER806 manufactured by Mitsubishi chemical corporation).

The content of the epoxy resin in the flux may vary depending on the phenolic resin and the benzoxazine compound present in the flux, and may be appropriately selected. In more detail, as described later, important are: the ratio of the number of moles of epoxy groups of the epoxy resin to the number of moles of phenolic hydroxyl groups of the phenolic resin to the number of moles of dihydrobenzoxazinyl rings of the benzoxazine compound is within a specified range.

In order to reduce the viscosity of the epoxy resin, it is preferable that the flux further contain a reactive diluent (also referred to as an epoxy reactive diluent) which is a low molecular weight epoxy resin. By adding a reactive diluent to the epoxy resin, the viscosity is not too high when the solder powder is subsequently added, and handling of the solder paste can be performed more easily. A paste-like solder paste can be prepared by adding a solvent to an epoxy resin, which can lower the viscosity of the epoxy resin and can be handled more easily when solder powder is added later, but a reactive diluent is preferably used to lower the viscosity of the epoxy resin, because the paste-like solder paste is reactive and thus is less likely to be involved in the reaction product of the epoxy resin and the curing agent and cause voids in the cured product.

As the reactive diluent, butyl glycidyl ether or 2-ethylhexyl glycidyl ether, which is an alkyl glycidyl ether system, can be used. These alkyl glycidyl ether compounds have a very low viscosity, and therefore, the effect of lowering the viscosity is large. However, the following problems exist: a problem that the volatility is high due to a low boiling point and the volatilization occurs due to heating at the time of curing; a problem that the crosslinking density is difficult to increase due to the monofunctional group and the rigidity of the cured product is difficult to exhibit; further, the moisture absorption rate is high, and therefore, it should be used in consideration of these circumstances.

Further, reactive diluents often contain a large amount of chloride ions due to their manufacturing process. The halogen ion represented by the chloride ion becomes a factor of an increase in leakage current in the electric and electronic parts. Chlorine contained in the reactive diluent is ionized by the intrusion of moisture, and causes leakage failure and corrosion of the electric and electronic parts. As a countermeasure against these problems, it is important to use a diluent in which the amount of chloride ions is reduced for the reactive diluent.

In view of such a point, examples of the reactive diluent include 1, 3-bis [ (2, 3-epoxypropyl) oxy ] benzene, dicyclopentadiene dimethanol diglycidyl ether, and N, N-bis (2, 3-epoxypropyl) -4- (2, 3-epoxypropoxy) aniline. More than 1 of these compounds may be used in combination. Of these, the reactive diluent is preferably 1, 3-bis [ (2, 3-epoxypropyl) oxy ] benzene.

1, 3-bis [ (2, 3-epoxypropyl) oxy ] benzene (the structural formula of formula 1 shown below) has a structure in which two epoxy groups are attached to both ends of a benzene ring of a stable skeleton. As an example of the reactive diluent substantially composed of 1, 3-bis [ (2, 3-epoxypropyl) oxy ] benzene, when the properties were measured by using EX-201-IM manufactured by NAGASECCHEMTEX, the viscosity was 400 mPas and the total chlorine amount was 0.04 mass%. Since 1, 3-bis [ (2, 3-epoxypropyl) oxy ] benzene has a rigid benzene ring, when it is used as a reactive diluent, it is assumed that the cured epoxy resin has a strong adhesion at room temperature and low moisture absorption.

[ solution 1]

(phenol resin)

The phenol resin contained in the flux contains 1 or more kinds of phenol resins having a phenolic hydroxyl group and an allyl group in the molecule. In particular, the phenolic resin preferably has 2 or more phenolic hydroxyl groups in 1 molecule which are capable of reacting with epoxy groups of the epoxy resin.

By including such a phenol resin in the flux, the flux can be made low in viscosity, and the handling of the solder paste can be performed more easily when the solder powder is added later. This is presumably because: the originally solid phenol resin is inhibited from being aligned by hydrogen bonds between phenolic hydroxyl groups due to the steric hindrance effect of the allyl groups of the phenol resin, and therefore, the viscosity of the phenol resin is reduced.

Among such phenol resins, a low-molecular-weight dimer (a structural formula shown in formula 2 (n is 0)) is particularly preferable because it is contained in the flux to exhibit a more suitable liquid state and can favorably reduce the viscosity of the solder paste. Specific examples of commercially available products include MEH8000H (viscosity of 1500Pa · s or more and 3500mPa · s or less and hydroxyl equivalent of 139 or more and 143 or less) manufactured by Minghuazai chemical Co., Ltd., and MEH8005 (viscosity of 4500Pa · s or more and 7500mPa · s or less and hydroxyl equivalent of 133 or more and 138 or less) manufactured by the same Co., Ltd.

[ solution 2]

A phenol resin having no allyl group may be used in combination with a phenol resin having an allyl group. As described above, it is presumed that the phenolic resin having an allyl group achieves a low viscosity due to steric hindrance of the allyl group. Further, similarly, the reaction between a phenolic hydroxyl group and an epoxy group tends to be slow due to the steric hindrance of an allyl group, and it is difficult to increase the crosslinking density. Therefore, the reactivity with an epoxy group can be improved by using a phenol resin having no allyl group in combination. When the reactivity with an epoxy group is increased and the crosslinking density is increased, the strength of the cured product can be increased and the adhesion of the solder paste can be improved. Among them, since the viscosity of the solder paste increases, it is necessary to appropriately adjust the amount of the phenol resin having no allyl group and the amount of the phenol resin having an allyl group.

Specifically, the phenol resin preferably contains a phenol resin having no allyl group in an amount of 40 mass% or less with respect to the entire amount of the phenol resin. By including the phenol resin having no allyl group in a content of 40 mass% or less, the viscosity of the solder paste can be prevented from excessively increasing.

The phenolic resin having no allyl group is not particularly limited as long as it has 2 or more phenolic hydroxyl groups in the molecule that can react with the epoxy resin. For example, polyfunctional phenols having 2 or more phenolic hydroxyl groups in the molecule, such as bisphenol a, phenol novolac, or cresol novolac, are preferable. In particular, from the viewpoint of solubility in other components of an epoxy resin or the like having 2 or more phenolic hydroxyl groups in the molecule, the phenolic resin preferably has a softening point of 60 ℃ or more and 110 ℃ or less and a hydroxyl equivalent of 70g/eq or more and 150g/eq or less. In the present application, the softening point refers to a temperature at which the phenolic resin softens and starts to deform due to a rise in temperature, and refers to a temperature measured by the ball-and-ring softening point measurement method. Further, in the present application, the hydroxyl group equivalent means a value measured by a neutralization titration method based on JISK 0070. Specifically, examples of commercially available products include phenol novolac resin (model H-4, manufactured by Ming & Chemicals), phenol aralkyl resin (model MEH-7800, manufactured by Ming & Chemicals), and biphenyl aralkyl resin (model MEH-7851SS, manufactured by Ming & Chemicals). Further, a phenol resin having only 1 phenolic hydroxyl group in the molecule may be used in combination.

The content of the phenol resin in the flux (the total amount of the phenol resin having an allyl group and the phenol resin not having an allyl group) may vary depending on the epoxy resin and the benzoxazine compound present in the flux and may be appropriately selected. In more detail, as described later, important are: the ratio of the number of moles of epoxy groups of the epoxy resin to the number of moles of phenolic hydroxyl groups of the phenolic resin to the number of moles of dihydrobenzoxazinyl rings of the benzoxazine compound is within a specified range.

(benzoxazine compound)

The benzoxazine compound is not particularly limited as long as it is a compound containing a dihydrobenzoxazine ring having a benzene skeleton and an oxazine skeleton (a structure in which N and O are present in the same ring of the oxazine skeleton, and one of two double bonds of oxazine is dihydrogenated and the other can be regarded as one side forming the benzene skeleton, also simply referred to as "benzoxazine ring").

In the benzoxazine compound, the chemical property of the dihydrobenzoxazine ring is stable and no chemical reaction occurs in the normal state. However, when heated to about 170 ℃ or higher, the dihydrobenzoxazine ring is opened to become a polybenzoxazine compound having a diaminodiphenyl structure containing a phenolic hydroxyl group and a basic amino group. It can be considered that: the basic amino group present in the diaminodiphenyl structure formed by the ring opening accelerates the reaction between the epoxy resin and the phenolic resin at the melting point of the solder powder at high temperatures (for example, about 219 ℃ in the case of SAC solder) or higher, and functions as a curing accelerator, thereby accelerating the curing of the resin after the solder is melted. Further, the dihydrobenzoxazine ring of the benzoxazine compound does not open until 170 ℃, and therefore, the reaction between the epoxy resin and the phenol resin does not occur, and thus the melting and aggregation of the solder, which will be described later, are not inhibited. After ring opening, the phenolic hydroxyl group can undergo self-polymerization or reaction with the epoxy resin or the like without generating a by-product. As described above, after the solder is melted, the flux reacts rapidly due to the ring opening of the dihydrobenzoxazine ring.

Here, as for a technique capable of lowering the reaction temperature of the resin to a low temperature region of about 150 ℃ or lower by adding a curing accelerator and a phenol resin to a composition mainly composed of a benzoxazine compound and an epoxy resin, for example, japanese patent laid-open nos. 2000-248151 and 2002-047391 are disclosed. When this technique is applied to the solder paste of the present embodiment, the solidification temperature of the resin becomes low, and the resin thickens before reaching a high melting point, thereby inhibiting melting and aggregation of the solder described later. However, according to the solder paste of the embodiment of the present invention, which has the epoxy resin and the phenol resin as the main components and contains the benzoxazine compound (and the activator) in other appropriate amounts, thickening does not occur until reaching a high melting point, and excellent solder connection can be performed.

In order to further improve the function as a curing accelerator, the benzoxazine compound is preferably a multi-oxazine having a plurality of dihydrobenzoxazine rings in the molecule.

The content of the benzoxazine compound in the flux may vary depending on the epoxy resin and the phenolic resin present in the flux, and may be appropriately selected. In more detail, as described later, important are: the ratio of the number of moles of epoxy groups of the epoxy resin to the number of moles of phenolic hydroxyl groups of the phenolic resin to the number of moles of dihydrobenzoxazinyl rings of the benzoxazine compound is within a specified range.

The benzoxazine compound has different structures due to different types of raw materials. In the present invention, benzoxazine compounds synthesized from various raw materials may be used. Alternatively, commercially available products may be used.

Typical commercially available compounds include the following compounds.

P-d type benzoxazine compound: polymer of phenol, diaminodiphenylmethane and formaldehyde (manufactured by four nations chemical industry Co., Ltd.)

[ solution 3]

(wherein R represents hydrogen or allyl.)

Further, the following compounds having different resin skeletons can be exemplified.

F-a type benzoxazine compound: bisphenol F Polymer with Aniline and Formaldehyde (manufactured by Siguo chemical industries Co., Ltd.)

[ solution 4]

Here, as described above, in the flux, an epoxy resin (if necessary, a low molecular weight epoxy reactive diluent), a phenol resin, and a benzoxazine compound are contained as main resins. As described above, polybenzoxazines obtained by ring-opening the dihydrobenzoxazine ring of the benzoxazine compound have an effect of accelerating curing of an epoxy resin and a phenolic resin. Here, it can be seen that: the flux preferably causes the epoxy resin and the phenolic hydroxyl group of the phenolic resin to react well with the dihydrobenzoxazine ring of the benzoxazine compound in a ratio of (the molar number of the epoxy group): (the molar number of the phenolic hydroxyl group): (the molar number of the dihydrobenzoxazine ring): 100: 50 to 124: 6 to 50.

The number of moles mentioned here is calculated by (mass of each component contained in the solder paste)/(molecular weight/number of functional groups). Further, based on the calculated number of moles, the number of moles of the epoxy group is set to 100, and other components are expressed by proportion calculation.

Here, when the number of moles of the phenolic hydroxyl groups is 50 or more relative to the number of moles of the epoxy groups 100, the amount of the epoxy groups is not excessive, so that unreacted epoxy groups do not remain, and crosslinking is favorably performed to form a cured product, whereby the reinforcing effect can be increased. When the ratio of the number of moles of the phenolic hydroxyl groups to the number of moles of the epoxy groups (100) is 124 or less, the phenolic hydroxyl groups do not become excessive, and can be prevented from becoming a plasticizer, and crosslinking can be favorably performed to form a cured product, whereby the reinforcing effect can be increased. When the number of moles of the dihydrobenzoxazine ring is 6 or more relative to the number of moles of the epoxy group 100, the effect of accelerating the curing of the epoxy resin and the phenolic resin is not reduced, and therefore, the reinforcing effect can be increased by favorably crosslinking the epoxy resin and the phenolic resin to form a cured product. When the ratio of the number of moles of the dihydrobenzoxazine ring to the number of moles of the epoxy group of 100 is 50 or less, the curing acceleration effect does not become excessively high, and the solder does not undergo thickening of the resin before melt aggregation occurs. The ratio of the above-mentioned number of moles is more preferably 100: 60 to 100: 7 to 40, and the ratio of the number of moles is more preferably 100: 70 to 90: 7 to 30.

When the balance of the ratio of the number of moles is calculated, the sum of the number of moles of the epoxy group, the number of moles of the phenolic hydroxyl group and the number of moles of the dihydrobenzoxazine ring preferably satisfies the following formula:

(active agent)

The type of the activator is not limited, and any suitable activator may be used as long as it has a function of removing the metal oxide film. For example, an organic acid, a halogen, an amine salt, or the like having a reducing power to remove an oxide film that may exist on the surface of electrodes, wirings, and/or solder powder of an electronic component as a component to be joined in a temperature region where a solder paste is heated may be used. Among these, in consideration of the poor insulation resistance of halogen to the cured epoxy resin and the poor storage stability of the paste due to the amine salt, the active agent is preferably an organic acid having excellent insulation and deterioration resistance characteristics. In particular, it can be suitably applied to electric/electronic applications. Alternatively, among amine-based active agents, Triethanolamine (TEA) is preferable because it has good reactivity and excellent preservability.

The organic acid has a particularly excellent flux action (here, flux action means a reducing action of removing an oxide film generated on the metal surface to which the solder paste is applied and an action of reducing the surface tension of the molten solder to promote the wettability of the solder on the joining metal surfaces). Further, regarding the reactivity with the epoxy resin, the organic acid does not exhibit reactivity comparable to the amine salt at room temperature, but exhibits high reactivity upon heating, and is therefore preferable. Further, since the organic acid is included in the cured product of the epoxy resin after the solder is reduced to remove the oxide film, the adverse effect such as corrosion hardly occurs.

The type of the organic acid is not particularly limited, and any organic compound acid can be used. For example, rosin component materials represented by rosin acids, various amines and salts thereof, sebacate salts, adipic acid, glutaric acid, succinic acid, malonic acid, citric acid, pimelic acid, and the like can be used. In particular, when considering the reaction with the epoxy resin, a dibasic acid which does not lower the crosslinking density is preferable.

The carboxyl group of the organic acid also reacts with the epoxy group at 200 ℃ or lower, and thus is involved in thickening of the flux in the solder paste. Therefore, when an organic acid is used as the active agent, the melting point of the organic acid is preferably 130 ℃ or higher and 220 ℃ or lower, more preferably 130 ℃ or higher and 200 ℃ or lower, and still more preferably 133 ℃ or higher and 186 ℃ or lower. This is because: by using the organic acid of the dibasic acid having a high melting point, melting and aggregation of the solder, which will be described later, are less likely to be inhibited.

Specifically, it is desirable that: in a solder having a high melting point such as SAC solder, the activation force (i.e., the reducing action for removing an oxide film on the surface of the solder) is small in a low temperature region of 130 ℃ or lower, and the activation force is exhibited in a high temperature region. Examples of the organic acid having a melting point of 130 ℃ or higher and 220 ℃ or lower include succinic acid (having a melting point of 186 ℃), adipic acid (having a melting point of 152 ℃), suberic acid (コルク acid) (having a melting point of 142 ℃), sebacic acid (having a melting point of 133 ℃) which are one kind of dibasic acid. Oxalic anhydride has a melting point as high as 189 ℃ but has high hygroscopicity, and forms a dihydrate having a low melting point (melting point of 101 ℃) due to moisture absorption. In addition, it is generally not expected that an organic acid having a melting point higher than that of SAC solder will remove the oxide film of solder as in isophthalic acid (melting point 340 ℃). However, these organic acids having a melting point of less than 130 ℃ or more than 220 ℃ are not intended to be excluded from the organic acids usable in the present invention, and may be suitably used depending on the actually used solder and reflow temperature, etc. These organic acids may be 1 component, or two or more components may be mixed.

The active agent is contained in a proportion of preferably 0.05% by mass or more and 60% by mass or less, more preferably 0.1% by mass or more and 50% by mass or less, and further preferably 0.2% by mass or more and 30% by mass or less, relative to the total mass of the flux. When the content of the activator (particularly, the organic acid) is in the above range, the flux action properly acts, and suitable connection reliability can be obtained.

(other Components)

Examples of other components contained in the solder paste include a modifier (for example, rosin) and an additive which are generally used. In addition, a solvent or diluent having a low boiling point may be added for the purpose of reducing the viscosity of the solder paste and imparting fluidity. Further, it is also effective to add hydrogenated castor oil, stearic acid amide, or the like as a thixotropy imparting agent for retaining the printed shape.

< solder powder >

The solder powder contained in the solder paste of the present invention is not particularly limited, and a solder powder having a melting point of 180 ℃ or higher, particularly 200 ℃ or higher is preferably used. The composition of the solder powder is not particularly limited, and may be in the form of a solder alloy. For example, SAC solder based on Sn, Sn-Cu solder, or Sn-Ag solder alloy can be used. Examples of SAC solder include SAC305(Sn-3.0Ag-0.5Cu) solder having a melting point of 219 ℃, SAC405(Sn-4.0Ag-0.05Cu) solder having a melting point of 220 ℃, and SAC105(Sn-1.0Ag-0.5Cu) solder having a melting point of 225 ℃. Examples of the Sn-Ag solder include Sn-3.5Ag solder having a melting point of 221 ℃, and examples of the Sn-Cu solder include Sn-0.7Cu solder having a melting point of 227 ℃. Among these solder alloys, SAC305 solder is preferable. This is because: nowadays, SAC305 solder is commonly used for consumer electronic devices, achieves high connection reliability and low cost, and is also commonly used for solder ball use of CSP, BGA packages.

The content of the solder powder is preferably 5 mass% or more and 95 mass% or less with respect to the total mass of the solder paste. By setting the content of the solder powder to 5 mass% or more, sufficient connection can be ensured. By setting the content of the solder powder to 95 mass% or less, the viscosity is not excessively high, and appropriate viscosity as a paste can be ensured, and a flux component can also be ensured, so that an appropriate reinforcing effect can be obtained. The content of the solder powder is more preferably in the range of 40 mass% to 95 mass%, and still more preferably 50 mass% to 95 mass%. By making the content of the solder powder in the above range, high connection reliability of the joint portion and excellent printing workability of the paste can be effectively achieved.

Alternatively, when the solder paste is used for connection between a SAC solder ball and an electrode of a circuit board, the content of the solder powder is preferably in a range of 5 mass% or more and 60 mass% or less with respect to the total mass of the solder paste. In the case of such connection, in metal bonding, the SAC solder ball becomes a main body, and the metal of the solder paste also assists the metal connection of the solder ball. Further, when the content of the solder powder is within the above range, the resin ratio in the solder paste becomes high, so that the periphery of the solder connection portion can be effectively reinforced with resin, and high connection strength can be exhibited. When the content of the solder powder is in the range of 60 mass% to 95 mass%, the metal content of the solder paste increases, and sufficient metal connection can be performed only by the metal component of the solder paste, and therefore, the present invention can be used in any case of using SAC solder balls (for example, BGA type) or not using SAC solder balls (for example, LGA type).

The composition of the solder powder in the present specification is expressed by the element symbol of the element included in the hyphen-connected solder powder. In the present specification, in order to describe the metal composition of the solder powder, a numerical value or a numerical range may be shown immediately before the metal element, and this is a case where% by mass of each element in the metal composition is represented by a numerical value or a numerical range as is generally used in the art (mass%). The solder powder may contain a trace amount of metal, such as Ni, Ge, Zn, Sb, and Cu, which is inevitably mixed, as long as the solder powder is substantially composed of the listed elements.

The melting point of the solder powder (or solder) in the present specification means: the melting completion temperature at the time of observing a change in state during the heating and temperature rise of the sample can be measured by DSC, TG-DTA, or the like.

Next, 1 example of a specific method of preparing a solder paste and a method of manufacturing (or manufacturing) a mounting structure by mounting an electronic component on a circuit board using the solder paste in the above-described embodiment of the present invention will be described.

First, the above epoxy resin, phenol resin, benzoxazine compound and activator were weighed and mixed to prepare a flux. Solder powder is added to the flux, and mixing and kneading are performed.

The solder paste according to the embodiment of the present invention can be used to mount a semiconductor component on a circuit board or the like having conductor wiring. A mounting structure, for example, a semiconductor device according to an embodiment of the present invention includes a bonding portion in which a terminal of a semiconductor component and an electrode of a circuit board are bonded using the solder paste. The solder paste can be applied by, for example, superimposing a metal mask having through-holes formed in the same positions as the electrodes on the circuit board, then supplying the solder paste to the surface of the metal mask, and filling the through-holes with a squeegee. Thereafter, if the metal mask is separated from the circuit board, the circuit board coated with the solder paste for each electrode can be obtained.

Next, the chip component or the semiconductor component is stacked on the circuit board using a chip mounter or the like so that the terminals of the chip component or the semiconductor component face the electrodes of the circuit board in an uncured state of the solder paste. Here, a chip resistor, a chip capacitor, or the like may be mounted as the chip component. As the semiconductor components, CSP or BGA formed with solder balls as terminals, semiconductor packages such as QFP formed with leads as terminals, or semiconductor elements (bare chips) formed with terminals without being housed in the packages can be used.

In this state, the printed circuit board on which the chip components are arranged is heated to a predetermined heating temperature in a reflow furnace. With this method, a semiconductor device according to another embodiment of the present invention including a conductive portion in which a terminal of a chip component or a semiconductor component and an electrode of a circuit board are connected by the solder paste according to the embodiment of the present invention can be manufactured. The conductive part is provided with: a solder joint portion (conductive portion) in which the solder powder and the solder ball are fused and integrated; and an epoxy resin cured part (reinforcing part) formed by covering the periphery of the cured flux with a cured product of the flux. As described above, according to the solder paste in the embodiment of the present invention, it is possible to manufacture a mounting structure in which the component and the substrate are electrically joined by the conductive portion and mechanically reinforced by the reinforcing portion.

In the reflow step, it is necessary to sufficiently melt the solder powder and sufficiently and appropriately perform a curing reaction of the resin component of the flux. Specifically, in the reflow step, when a curing reaction of an epoxy resin, which is a flux component in the solder paste, occurs before the solder powder is completely melted, the flux is thickened. This prevents the solder particles from being aggregated and melted, and does not exhibit proper metal conduction. To avoid this, the temperature of the reflow furnace needs to be raised to the melting point of the solder powder to be used, the curing reaction of the resin is slow, the solder powder is melted, and after the resin is fused and bonded to the solder ball of the semiconductor component and the electrode metal of the circuit component, for example, the resin of the flux finishes the curing reaction in a short time (for example, several minutes or so).

In the solder paste according to the embodiment of the present invention, the flux is made to contain the epoxy resin and the phenol resin as main components and further contain an appropriate amount of the benzoxazine compound (and the activator), so that the flux is less likely to be thickened until the temperature of the reflow furnace is raised to the melting point of the solder powder in the solder paste (particularly, the melting point of the SAC305 solder, which is about 219 ℃). Further, by using an appropriate amount of an activator in combination with the composition of the flux, excellent solder fusibility and short-time solidification of the resin flux after solder melting can be achieved.

In another embodiment, the solder may be melted in a reflow furnace, and then the temperature may be lowered to 150 to 200 ℃ to perform a two-stage process of mild solidification. In this case, when only the ring-opened benzoxazine compound and the activator are used, the curing rate is lowered, and therefore, a curing accelerator may be used in combination in an appropriate amount to the extent that melting of the solder is not impaired. Examples of the curing accelerator include cyclic amines such as imidazoles, tertiary amines and DBU salts, triarylphosphines such as TPP salts, quaternary phosphonium salts, and metal complexes such as iron acetylacetonate. Among these, a high-temperature reaction system is suitable.

Fig. 2A to 2C are cross-sectional explanatory views schematically showing a bonding process of a ball portion of the CSP using the solder paste in the embodiment of the present invention. As shown in fig. 2A to 2C, the electrodes 2 provided on the CSP substrate 1 and the electrodes 4 provided on the circuit board 3 are bonded together with solder balls 8 and solder paste 7, and then heated and cured by a dryer 9. The periphery of the formed conductive part 5 is reinforced by a reinforcing part 6b which is a cured solid epoxy resin. Fig. 2D is an image of a cross section of a solder bonding portion of the CSP bonded with the solder paste in the embodiment of the present invention. As described above, the periphery of the conductive portion 5 is reinforced by the reinforcing portion 6b containing the cured resin.

Fig. 3A to 3C are cross-sectional explanatory views schematically showing a chip component bonding process using the solder paste in the embodiment of the present invention. As shown in fig. 3A to 3C, a chip component 10 is mounted on the solder paste 7 applied to the electrodes 4 provided on the circuit board 3, and is heated and cured by a dryer 9. Thereby, the solder is melted and connected to form the conductive portion 11, and the liquid epoxy resin 6a pushed out by the force of the solder to gather covers the periphery of the solder and/or the lower portion of the chip component 10. Thereafter, the resin is cured by heating to form the reinforcing portion 6b as a solid epoxy resin, thereby completing the present invention. In this manner, a mounting structure is manufactured which has the conductive portion 11 in which the chip component 10 and the circuit substrate 3 are metal-bonded (metal-bonded of metal including solder powder in solder paste derived from the raw material) and the reinforcing portion 6b around the conductive portion 11.

Examples

Examples of the present invention and comparative examples are shown below. The embodiments of the examples and comparative examples of the present invention described below are merely illustrative and do not limit the present invention. In examples and comparative examples, "parts" and "%" are based on mass unless otherwise mentioned.

< preparation of solder paste >

First, an epoxy resin, a phenol resin, and a benzoxazine compound were weighed so as to occupy the mass parts shown in fig. 4 and 5, respectively, and heated and melted to 140 ℃. After cooling to room temperature, the weighed organic acid was further added and mixed by using a planetary mixer, to prepare fluxes of examples 1 to 10 and comparative examples 1 to 3.

Bisphenol F type epoxy resin (model JeR806, Mitsubishi chemical) was used as the epoxy resin. As the epoxy-reactive diluent, 1, 3-bis [ (2, 3-epoxypropyl) oxy ] benzene (the structural formula of formula 1 described above) (manufactured by NAGASE CHEMTEX corporation: EX-201-IM) was used. The phenol resin used was allyl-modified phenol novolac (product of Minghe Kasei corporation: model MEH 8000H). As a phenol novolac for general use, phenol novolac (manufactured by Minghe chemical Co., Ltd.: type HF-1M or H-4) is used. P-d type benzoxazine (manufactured by Sichuan chemical industry Co., Ltd.) or F-a type benzoxazine (manufactured by Sichuan chemical industry Co., Ltd.) was used as the benzoxazine compound. As the active agent, sebacic acid (manufactured by tokyo chemical industry corporation), adipic acid (manufactured by tokyo chemical industry corporation) or Triethanolamine (TEA) (manufactured by tokyo chemical industry corporation) was used.

Next, solder powder was added to the flux of examples 1 to 10 and comparative examples 1 to 3 obtained in the above manner in such proportions as to occupy the parts by mass shown in fig. 4 and 5, respectively, and further kneaded to prepare a solder paste. The solder powder used was SAC305 solder powder (Sn-3.0Ag-0.5Cu) (average particle size: 10 to 25 μm, melting point: 219 ℃ C. (manufactured by Mitsui Metal mining Co., Ltd.)) or SAC105 solder powder (Sn-1.0Ag-0.5Cu) (average particle size: 10 to 25 μm, melting point: 225 ℃ C. (manufactured by Mitsui metal mining Co., Ltd.)).

< preparation of evaluation device for adhesion >

The solder paste prepared as above was printed on the Au-plated electrode on the circuit substrate (FR-4 substrate) using a metal mask in such a manner that the thickness reached 0.1mm, forming a solder paste printed portion.

And, a chip resistor (tin electrode) having a size of 3.2mm × 1.6mm was mounted to the solder paste printed portion on the circuit substrate using a chip mounter. The electrode material of the circuit board is copper, and the substrate material is glass epoxy. Thereafter, a junction portion was formed by heating at 240 ℃ for 6 minutes using a reflow apparatus, and an evaluation element was produced.

< evaluation >

The evaluation was performed on examples 1 to 10 and comparative examples 1 to 3 according to the following items. The evaluation results are shown in fig. 4 and 5 as characteristics of the solder paste in each example.

(printability)

Evaluation of the printability of the solder paste was performed by observing the shape of the solder paste printed using the metal mask. The observation was performed by visually observing the convergence state to the electrode region, the sagging state, or the shape of the cusp. Evaluation of printability was determined by the shape of the paste when it was transferred onto the electrode of the circuit board through the through-hole of the mask. The electrode portion can be described as "o" when it retains its shape, as "Δ" when it can be used although its shape is defective (sagging or sharp protrusions are generated), and as "x" when it is very poor in shape.

(Adhesivity)

Fig. 6 is a schematic cross-sectional view illustrating a method of measuring shear adhesion force of a chip component. The adhesion strength was measured by fixing the chip component 10 to a heatable stage 13 and pushing it horizontally using a shear jig 12. The adhesion of the solder paste was evaluated by measuring the shear adhesion force at room temperature of 20 ℃ of the adhesion evaluation element produced as described above using a bonding test apparatus (Series 4000, manufactured by DAGE corporation) measured in this way. In the evaluation of the adhesion, the load applied to the joint portion was regarded as "excellent" when the chip was not broken even if it exceeded 30 Kg/chip, as "good" when the chip was broken in the range of 20 to 30 Kg/chip, as "delta" when the chip was broken in the range of 10 to 20 Kg/chip, and as "x" when the chip was broken in the range of less than 10 Kg/chip.

(metallization)

The metallization (solder joint reliability) was evaluated in accordance with the following JIS Z3284-4 solder ball test. When the degree of aggregation of the solder is rated 1, it is rated 2, it is rated x, when the degree of aggregation of the solder is rated 3, it is rated Δ, and when the degree of aggregation of the solder is rated 4. The details of each stage of the aggregation degree of the solder are as follows.

Level 1: the solder (powder) melts and the solder becomes a large ball with no solder balls around it.

And 2, stage: the solder (powder) melts, and the solder becomes a large ball having three or less solder balls with a diameter of 75 μm or less.

And 3, level: the solder (powder) melts, and the solder becomes a single large sphere, and has four or more solder balls with a diameter of 75 μm or less around the sphere, and is not arranged in a semi-continuous ring shape.

4, level: the solder (powder) melts, and the solder becomes a large ball, and a plurality of fine balls are arranged in a semi-continuous ring around the large ball.

(comprehensive judgment)

In the three evaluations of printability, adhesiveness and metallization, all the items were marked as "o", Δ in the case of 1 Δ, and "x" in the case of 1 ×, and the overall evaluation was performed.

The blending amounts shown in fig. 4 and 5 represent parts by mass. The BOZ ring represents a dihydrobenzoxazine ring.

For example, as shown in fig. 4, SAC305 solder was used as the type of solder powder in example 1. The solder powder was 266 parts by mass, the flux was 55.5 parts by mass, and the solder ratio was 82.0%. The epoxy resin in the flux was jER806, and the amount added was 22.0 parts by mass. The reactive diluent was EX-201-IM, and the amount added was 6.0 parts by mass. The phenolic resin was MEH8000H, and the amount added was 18.5 parts by mass. The benzoxazine compound was P-d type, and the amount added was 4.0 parts by mass. Sebacic acid was used as an activator, and the amount was 8.0 parts by mass.

In example 1, the epoxy equivalent (molecular weight/number of functional groups) of the jER806 was 160, and therefore, the number of moles of epoxy groups in the epoxy resin was 0.14 mol. Similarly, since the epoxy equivalent (molecular weight/number of functional groups) of the reactive diluent (epoxy reactive diluent) is 120, the number of moles of epoxy groups reaches 0.05 moles. Therefore, the total mole number of epoxy groups is 0.19 mole. By the same calculation, the phenolic hydroxyl group of the phenolic resin was 0.13 mol. In addition, the number of moles of dihydrobenzoxazine rings of the benzoxazine resin reached 0.02 mol. When the molar number of epoxy groups, the molar number of phenolic hydroxyl groups, and the molar number of dihydrobenzoxazine rings is 100, the ratio of the molar number of phenolic hydroxyl groups to the molar number of dihydrobenzoxazine rings is 100: 70: 10, respectively, when the molar number of epoxy groups is 100.

In the evaluation results of the solder paste of example 1, the printability was good and the evaluation was evaluated as o. The adhesion was 28 Kg/chip, and the determination was O. The metallization was good at grade 2, and rated as O. As a result, the overall judgment was also ∘. With respect to the solder pastes of examples 2 to 10 in which the kinds and amounts of the solder powder, the epoxy resin, the phenol resin (including MEH8000H having allyl as an essential component), the benzoxazine compound and the organic acid were variously changed, evaluation of the printability, the adhesiveness and the metallization property of good or usable grades was similarly confirmed as shown in fig. 4.

Comparative example 1 used a solder paste containing no activator. The evaluation results showed that the printability was good, but the solder did not melt, and the metallization was rated 4, which was judged as x. The resin was cured, but the strength of the metal joint was insufficient, and the adhesion was as weak as 9 Kg/chip, and was judged as X. From the results, the total was judged to be X.

Comparative example 2 used a solder paste containing no phenolic resin. The evaluation results showed that the printability was good, but the adhesion was poor. The total judgment was also X. This is presumably because: a phenolic resin in which a curing agent that reacts with an epoxy resin is not present, but a benzoxazine compound reacts with an epoxy resin to some extent, and thus exhibits some adhesiveness.

Comparative example 3 used a solder paste containing no benzoxazine compound. The evaluation results showed that the printability was good, but the adhesion was poor. The total judgment was also X. This is presumably because: there is no benzoxazine compound that promotes the reaction of the epoxy resin with the phenolic resin and thus curing is not performed.

Fig. 7 is a graph showing the measurement results of the shear adhesion force of the chip component in the example of the present invention. As shown in fig. 7, it can be seen that: when example 1 is compared with comparative examples 1 to 3, it is important for adhesion that the solder paste containing the solder powder and the flux contains at least an epoxy resin, a phenolic resin, a benzoxazine compound, and an activator, and that the phenolic resin contains a phenolic resin having a phenolic hydroxyl group and an allyl group in the molecule.

When the results of fig. 4 and 5 are examined, a solder paste containing an epoxy resin and a phenol resin as main components and further containing a benzoxazine compound as a flux component has excellent adhesion in a reflow soldering process at 240 ℃. This is presumably because: the benzoxazine compound is heated at 170 ℃ or higher to open a dihydrobenzoxazine ring to a polybenzoxazine compound having a diaminodiphenyl structure, and a basic amino group present in the diaminodiphenyl structure formed by the opening of the ring promotes a reaction between an epoxy resin and a phenol resin. In addition, it is presumed that excellent adhesion is also ensured by the formation of a crosslinked structure by the reaction of the hydroxyl group of the epoxy resin itself.

Such a change to the polybenzoxazine compound under reflow conditions occurs after melting of the SAC solder, and therefore, the flux is difficult to thicken before melting of the SAC solder. Therefore, it is presumed that the solder is very suitable for melting and joining of solder. Further, since the ring opening of the dihydrobenzoxazine ring of the benzoxazine compound hardly occurs at low temperature, the solder paste has very stable room-temperature storage property and has a long pot life at room temperature.

It can be further assumed that: when 1 or more types of phenol resins having phenolic hydroxyl groups and allyl groups in the molecule are used, the viscosity becomes low at room temperature due to the effect of the allyl groups, the curing rate becomes slow, and as a result, the melting property of the solder becomes good.

If the results of fig. 4 and 5 are further examined, it can be seen that: the ratio of the number of moles of epoxy groups to the number of moles of phenolic hydroxyl groups to the number of moles of dihydrobenzoxazine rings in the epoxy resin, the phenolic resin, the benzoxazine compound and the activator contained in the flux for solder paste is preferably 100: 50 to 124: 6 to 50 (the number of moles of epoxy groups): (the number of moles of phenolic hydroxyl groups): (the number of moles of dihydrobenzoxazine rings).

Industrial applicability

The solder paste and the mounting structure of the present invention can be used for a wide range of applications in the field of electric/electronic circuit forming technology. The resin composition can be used for connecting electronic parts such as CCD elements, hologram elements, chip parts and the like and for bonding them to substrates. Further, the present invention can be used for products incorporating these elements, components, or substrates, for example, DVDs, mobile phones, portable AV devices, digital cameras, and the like.

Claims

1. A solder paste comprising solder powder and flux,

the phenolic resin contains 1 or more phenolic resins having phenolic hydroxyl groups and allyl groups in the molecule.

2. The solder paste according to claim 1, wherein a ratio of the number of moles of epoxy groups contained in the epoxy resin to the number of moles of the phenolic hydroxyl groups to the number of moles of dihydrobenzoxazine rings contained in the benzoxazine compound is

3. A solder paste according to claim 2, wherein the sum of the number of moles of the epoxy group and the number of moles of the phenolic hydroxyl group and the number of moles of the dihydrobenzoxazine ring satisfies the following formula:

4. A solder paste according to any one of claims 1 to 3, wherein the phenolic resin contains a phenolic resin having no allyl group in an amount of 40 mass% or less relative to the entire amount of the phenolic resin.

5. A solder paste according to any one of claims 1 to 4, wherein the benzoxazine compound is a poly-oxazine having a plurality of dihydrobenzoxazine rings within the molecule.

6. A solder paste according to any one of claims 1 to 5, wherein the solder powder is a Sn-Ag-Cu-based solder or a Sn-Cu-based solder having a melting point of 200 ℃ or higher.

7. A solder paste according to any one of claims 1 to 6, wherein the solder powder is contained in a proportion of 5 mass% or more and 95 mass% or less with respect to the total mass of the solder paste.

8. A solder paste according to any one of claims 1 to 7, further comprising a reactive diluent,

the reactive diluent is 1, 3-bis [ (2, 3-epoxypropyl) oxy ] benzene.

9. A solder paste according to any one of claims 1 to 8 wherein the activator is an organic acid,

the organic acid has a melting point of 130 ℃ or higher and 220 ℃ or lower.

10. A mounting structure for mounting an electronic component on a circuit board using the solder paste according to any one of claims 1 to 9, comprising: